Pressure vessels for energy exchange devices such as heat exchangers have been in industrial use for long time. In the last 10-15 years a new energy exchange device termed a pressure exchanger has been commercialized. This device has adapted standard commercial composite pressure vessels used for membrane separation by reverse osmosis.
Such pressure vessels are designed for the insertion of single or multiple membrane modules from both ends without removing the pressure vessel, but this is not a requirement as housing for an energy exchange device. Hence it becomes a bulky solution with multiple seals needed for the inlet and discharge of two different fluid streams. Such seals tend to develop leaks over time and need replacement.
Composite vessels need to be oversized and heavy to account for the gradual fracturing of reinforcement fibers over perhaps a life of 25 years. In order to secure end caps the vessel need to be extended substantially, which account for a large loss of productive volume since only a short net length is required for an energy exchange device.
In addition it is desirable to arrange either the inlet or discharge flow through a side port of the pressure vessel. For a composite vessel this becomes particularly challenging as such a port cannot have a very large diameter without substantial increased wall thickness, added weight and cost.
U.S. Pat. No. 7,306,437 discloses a pressure exchanger having a metal pressure vessel with thin walls that accommodate cast or welded in 2 side ports. The pressure vessel is made of a section containing three of the four ports, while the end cap provides the fourth port.
Although this design eliminates many of the concerns with using composite pressure vessels, it has some important limitations. The design does not allow for radial flow through side ports of low pressure fluid, which is desirable in order to integrate a circulation pump for the high pressure stream. Direct low pressure flow through a side ported ceramic end cover poses difficult sealing issues and/or an destructive asymmetric side load of the end cover.
Furthermore, the long vessel imposes manufacturing issues in terms of internal machining and size when casting.